I'm a Google Apps admin, and it's a mystery that, anytime I receive a message from just one specific ALIAS or GROUP address (and that I'm a member of that group or alias), it RE-SENDS the same message back me AGAIN, placing a new copy in my SENT mailbox. This results in my SENT mailbox filled with tons of emails I never intended to send. Worse, this is an address I've used to sign up for a ton of newsletters, that I want multiple people to receive.

I'm not sure where to start analyzing this. Here's what I have as conditions and hints:

I'm the admin on the G Suite account, so I have complete access to change anything. (But, need some ideas or tests to try).

I've checked and rechecked all my filters, and there is no reference to this alias at all, so it isn't visible.

At one point I was messing around with some Google scripts/apps[?] - Any chance I could have some long forgotten script that is messing up??

I've long since attempted and failed to just get all my SENT messages from my main email address to be automatically filtered to my in-box, so I've had to remember the practice of adding a CC to myself to make this happen automatically.

If you were playing with Apps Script, you can find them by going to drive and searching for type:script and that will show all your App Script files.
– tyelfordMay 9 '17 at 4:32

Thanks @tyelford -- it made checking out my scripts easy. Unfortunately, there's nothing even close to causing this in my scripts. Maybe I will kill, and then recreate it "group". NEXT possibility -- Some ADD-ON plugin, "Gadget", or app that I added to my Gmail...
– DaaBossMay 9 '17 at 23:42

@Folk - Thanks for the advice. It WOULD have been really cool. However, we have a legacy Google Apps account, and evidently, this logging is not available: "Admin console dashboard, go to Reports / Audit /Email log search". Got to "Reports / Audit", but nothing with email or log search at all. SO, "I cheated", and deleted the group, and recreated the group, and added back the identical two members, and so far, it appears that it will NOT put another copy of that email in my OUT mailbox. Why?? No clue, but at least this works. It would have been fun to figure it out. Thanks Again.
– DaaBossMay 10 '17 at 20:26